1. Field of the Invention
The present invention relates to a radio mobile communications system using the time-division multiple-access (TDMA) scheme and, more specifically, to a power saving technique for use in a radio base station in the radio communications system.
2. Description of the Related Art
The time-division multiple-access/time-division duplex (TDMA/TDD) scheme is a form of TDMA scheme and is advantageous where frequency management is readily made and transmitting/receiving is performed without the need of a pair of frequency bands or a diplexer because alternating time slots on the same carrier signal are assigned to the forward and reverse directions of communication. A further advantage of the TDMA/TDD scheme is that diversity can be made only at the side of a base station. The TDMA/TDD scheme has been used in Japan for personal handy-phone system (PHS) and in Europe for the digital European cordless telephone (DECT).
In a radio mobile communications system, power saving control is necessary for radio base stations and mobile terminals. Since power consumption for transmitting radio signals is usually large, there have been proposed several transmission power control methods.
For example, a transmission power controller has been disclosed in Japanese Patent Unexamined Publication No. 7-336291. The transmission power control is performed depending on both the bit error rate and the electric field level of a received signal. More specifically, the transmission power is reduced when the bit error rate is lower than a threshold or when the received electric field level is greater than a threshold.
However, it is difficult to further reduce in power in the case of diversity-combining base station or high-traffic base station. The diversity-combining base station needs a plurality of receiving branches for diversity combining and the high-traffic base station needs a plurality of radio transceivers to cope with high volumes of traffic. Therefore, the power consumption required for receiver circuits forms an increased proportion of the entire power consumption of the base station and further reduced power consumption cannot be achieved by controlling the transmission power consumption only.
The base station with a large amount of power consumption would rapidly run out a backup battery in the event of a power failure and further lead to increased heat generation.
The inventor found that it still has plenty of room for reduction in power consumption of a base station from the viewpoint of receiving operation in the TDMA scheme.
An object of the present invention is to provide power saving method and apparatus that can achieve a substantial reduction in total power consumption of a radio base station.
According to an aspect of the present invention, in a mobile communications system using a time-division multiple-access (TDMA) format, an occupied time slot is discriminated from an idle time slot in a frame to produce a discrimination signal. A power control signal for a receiver is switched between a first state and a second state in time slots depending on the discrimination signal. The power control signal is switched to the first state at timing of the occupied time slot and to the second state at timing of the idle time slot.
According to another aspect of the present invention, a radio base station includes a radio section including a plurality of receivers and a power supply for supplying power to the radio section. Further, it is provided with a discriminator for discriminating between an occupied time slot and an idle time slot in a frame to produce a discrimination signal and a controller for switching a power control signal between a first state and a second state in time slots depending on the discrimination signal, wherein the power control signal causes the power supply to operate.
Each of the receivers may include an analog signal section including a radio-frequency amplifier for amplifying a radio-frequency analog signal, a frequency converter for converting the radio-frequency analog signal to an intermediate-frequency analog signal by mixing it with a local oscillation signal, and an intermediate-frequency amplifier for amplifying the intermediate-frequency analog signal, a frequency synthesizer for generating the local oscillation signal, and a modem section including a demodulator for demodulating the high-frequency analog signal to produce a digital signal and a decoder for decoding the digital signal to produce received data.
The controller switches the power control signal to the first state at timing of the occupied time slot and switches the power control signal to the second state at timing of the idle time slot. The first state causes the receiver to be powered on and the second state causes the analog signal section of the receiver to be powered off and the frequency synthesizer and the modem section to be in a standby mode.
As described above, since each receiver of the radio base station is subjected to power switching control in time slots depending on the discrimination signal, the total power consumption of the radio base station can be reduced compared with the prior art. Such reduction In power consumption causes the backup battery to be prevented from rapidly exhausted in the event of a power failure. Further the reduction in power consumption also decreases heat generation.